1. Field of the Invention
This invention relates to making an electrical contact by treating a metallic substrate prior to depositing a protective layer thereon.
2. Description of the Prior Art
The deposition of a metal onto a metallic substrate, typically accomplished by electroplating from an electrolytic solution, is used in a variety of industries for a variety of purposes. For electrical and electronic components such as switch contacts, relay contacts, printed circuit board contacts, integrated circuit contacts, etc., a layer of a protective metal is deposited onto a substrate metal. The protective metal typically reduces corrosion of the substrate material. This helps maintain low electrical resistance to the substrate material, which is important for electrical contacts. The protective metal is typically a precious metal, such as gold, silver, platinum, etc., and the substrate metal is typically nickel, copper, etc., and alloys thereof.
In order to prepare the substrate for the subsequent metal deposition, it is desirable to minimize surface inhomogeneities on the substrate. This is often accomplished by chemical or electrochemical polishing of the substrate prior to electroplating. With the recent advent of continuous strip processing of electrical connectors, both the electropolishing and electroplating steps are typically accomplished in one continuous operation; see, for example, U.S. Pat. No. 4,153,523, assigned to the same assignee as the present invention. Other methods of preparing substrates include flame melting, wherein gross surface inhomogeneities are reduced in magnitude. Mechanical polishing or grinding steps may also be taken to prepare substrates for plating.
With the increased cost of certain plated metals, including gold, it has become especially desirable to find ways or reducing the amounts of such plated metal necessary to protect the substrate. Therefore, it is desirable to find improved methods of preparing substrates prior to depositing a protective layer thereon, in order to reduce the amount of protective metal required. To be compatible with a continuous high-speed strip plating process, as that noted above, any substrate preparation technique should be capable of sequential, high-speed treatment of substrates. Furthermore, with the trend toward selective plating in order to conserve precious metals, any treatment desirably is capable of treating selected areas of substrates.